1. Field of the Invention
The present invention generally relates to a fixing apparatus to fix a toner image on a recording medium by using a fixing solution and an image forming apparatus such as a copier, a multifunction peripheral, a printer, and a facsimile machine, which includes the fixing apparatus, and more specifically, to a configuration to efficiently attach a fixing solution to unfixed toner carried on the recording medium.
2. Description of the Related Art
In recent years, there have been various apparatuses to form images on recording paper, such as a copier, a printer, and a facsimile machine. Among these apparatuses, an electrophotographic type image forming apparatus that uses toner has been predominantly used in offices and the like since images can be formed on normal paper at high speed with high density, and recently, even color images can be easily formed on recording paper. Most of the electrophotographic type image forming apparatuses employ heat to fix images. By this method, a roller, a film, and the like heated by a heating element such as a halogen heater and a ceramic heater sandwich recording paper having unfixed toner on the surface, to heat and pressurize the recording paper. As a result, the unfixed toner is fused and deformed, and fused (anchored) into fibers of the recording paper to be fixed therein.
This method is widely used because of advantages in that images are formed with high uniformity and the image forming apparatus is stably operated, however, there is a disadvantage of consuming too much power. To solve this problem, a heating method and a vapor fixing method have been employed as a method for fixing toner (for example, see Patent Document 1).
By the vapor fixing method, recording paper having unfixed toner on the surface is exposed to solvent vapor that melts toner, thereby the unfixed toner is swollen or dissolved so as to be fixed on the recording paper. This method requires less power consumption than the heating method; however, a liquid used as the solvent to dissolve the toner is odiferous or may have an adverse effect on a human body. Therefore, this method has failed to be a predominant method.
In recent years, with a development of a non-odiferous solution that has no adverse effect on a human body, and can swell or dissolve toner to be fixed, a fixing method by using a solution has started to be used again. There have been disclosed many ways to supply a solution, which is non-odiferous and has no adverse effect on a human body, and swells or dissolves toner, on a recording medium carrying unfixed toner.
For example, a wet fixing method to fix toner has been disclosed (for example, see Patent Document 2). In the wet fixing method, an oil-in-water type (O/W type) fixing solvent which can dissolve or swell toner is used. The oil-in-water type fixing solvent is formed by dispersively mixing an organic compound, which cannot be dissolved or hardly dissolved in water, with water. The wet fixing method is performed such that the oil-in-water type fixing solvent is sprayed or deposited in drops onto a surface of an object having unfixed toner at a predetermined position so that the unfixed toner is dissolved or swollen, and then the object is dried.
By performing the wet fixing method, however, toner that is only electrostatically attached to the recording paper may be moved depending on a diameter of the droplets of the sprayed or deposited fixing solvent and a speed at which the droplets of the fixing solvent and toner are collided with each other (kinetic energy). Therefore, an image may be formed with a defect.
In view of the above problems, a fixing apparatus using an electrostatic force has been disclosed (for example, see Patent Documents 3 and 4). In the fixing apparatus, a fixing solution is charged with an opposite polarity to that of the toner so that the fixing solution is attached to the toner by a coulomb force generated with the toner. Therefore, a speed at which the toner image and the fixing solution are collided with each other can be moderated comparing to the above-described fixing method. As a result, since the kinetic energy can be decreased, probability that an image is formed with a defect due to a moved toner image is reduced.
[Patent Document 1] Japanese Published Examined Patent Application No. S40-10867
[Patent Document 2] Japanese Patent No. 3290513
[Patent Document 3] Japanese Patent Application Publication No. 2006-163083
[Patent Document 4] Japanese Patent Application Publication No. 2007-121448
According to the configurations disclosed in Patent Documents 3 and 4, however, droplets of a fixing solution are carried to an opening by using a fan, and attached onto toner through the opening. Therefore, droplets of the fixing solution which are apart from the surface having the toner image are more likely to be influenced by an air flow of the fan, than the coulomb force, while droplets which are close to the surface having the toner image are influenced by the coulomb force. Thus, the droplets of the fixing solution cannot be efficiently attached to the toner image.
The present invention is made in view of the abode-described problems, and it is an object of at least one embodiment of the present invention to improve attachment efficiency between a fixing solution that softens or melts toner and unfixed toner carried on a recording medium, and to prevent an image from being formed with a defect.